Positioning-related timing measurements represent an area of current and growing interest, as wireless communication networks increasingly provide or otherwise support positioning functions. Such measurements include but are not limited to Time-of-Arrival (TOA) measurements on signals to/from mobile stations and base stations. Other examples of timing measurements are timing advance (TA), Round Trip Time (RTT) and one way propagation delay. In a particular example, a mobile station uses a downlink signal received from a reference cell to establish a reference timing, and then determines additional timing values for the downlink signals received from one or more other cells. The mobile station may determine the relative timing of these other signals with respect to the reference cell, as a basis for determining the mobile station's positioning, or may provide the raw timing values to another node (e.g., a base station and/or positioning node) for such a determination.
Taking the example of a network based on the Long Term Evolution (LTE) standards promulgated by the Third Generation Partnership Project (3GPP), multiple positioning methods to support “Location Based Services” (LBS) may be used separately or in some combination. The particular method(s) depends on where the measurements are to be performed and how the final position is to be calculated. Further variables include how quickly the measurement is to be provided and at what level of accuracy or uncertainty.
Examples include UE-based measurements, where the timing measurements are made at the user equipment (UE); UE-assisted measurements, where the timing measurements are not made at the UE, at least not in final form, but the UE provides assistance data, such as raw timing data. Additionally, LTE provides for network-based measurements, such as where measurements are made by the eNodeB or at another network node (such as a positioning node). LTE further provides for network-assisted timing measurements, where the network does not perform the timing measurements but does provide data aiding or otherwise enabling those measurements, e.g., at a UE.
In more detail, the LTE location architecture defines an “evolved serving mobile location center,” which is referred to as an “E-SMLC.” The E-SMLC functions as a server for supporting or performing positioning activities. A mobility management entity (MME) in the LTE core network provides positioning requests to the E-SMLC, and the E-SMLC in turn configures the LTE device, such as a UE, for performing one or more positioning measurements. The configuration of the UE is carried out by using signaling which follows the LTE Positioning Protocol, referred to as “LPP.” To support positioning operations, LPP supports the exchange of (measurement) capability information, assistance data to aid the positioning-related measurements, such as signal timing measurements, and location information that may be exchanged either as the measurements necessary to determine location, or the location determination.
For LTE and other network types, making accurate timing-related measurements is becoming increasingly challenging as the radio service configurations of such networks become more complex. For example, network capacities are being increased through the use of multi-carrier arrangements where multiple carriers at different frequencies are used to serve a larger numbers of users thin the same cell and/or to provide users with higher aggregate data rates. Similarly, different uplink and downlink frequencies, or sets of such frequencies, may be used in the same cell or across neighboring cells. Making accurate relative timing measurements on a mix of uplink and downlink signals, or across signals at substantially different frequencies, introduces a number of significant complications that are not well addressed using conventional approaches to timing measurement.